Various endoscopic techniques and devices are known for treating a prolapsed intervertebral disc in the spine. Basically, for example, after an incision has been made in the skin of the patient, first of all an elongate element with a tapered rounded tip is inserted (percutaneously), the purpose of which is adaptation of the soft tissue as far as into the immediate vicinity of the damaged disc requiring repair. Once this first elongate element has been introduced, a fine cannula is introduced thereover, the internal diameter of which matches the external diameter of the first elongate element. The external diameter of the cannula may be between 2 mm and 10 mm, with cannulae being used most frequently which have a diameter of approximately 6 mm. This cannula comprises a round cross-section and may have different shapes at its distal end, the distal end generally being bevelled in shape relative to the axis of the cannula, to allow a better view of the working area. After introduction of the cannula the first elongate element is removed, leaving an open access channel to the damaged disc, an optical probe (endoscope) being introduced, which is conformed to this channel and which in turn has channels for pressurized water for cleaning purposes and for sucking out material and working channels for working instruments, such as forceps or the like, for treating and working on the (disc) tissue.
However, the problem may arise that bone tissue or bony growths are present in the working area which hinder the cannula from advancing as far as into the region of the disc to be treated or which have a troublesome effect on the orientation of the cannula with regard to the working area. Often it is necessary, therefore, to use a cutting tool to cut or file away bone tissue so as to obtain access to the site needing treatment.
The techniques which are currently known offer two different solutions to this problem. The first one involves a cutting tool of a size which allows it to be introduced through a working channel of the optical probe. This solution allows the user to remove bone tissue while maintaining visual observation of his actions. However, the problem arises here that the tool has necessarily to have a very reduced diameter (maximum diameter 3.5 mm) and the process of removing bone tissue may take too much time, which is disadvantageous to the patient. The second known solution involves removal of the optical probe and use of a cutting tool with a larger diameter. The difficulty here is that the user has to undertake the intervention without a direct view of the soft tissue present, with the attendant risk of injury to nerve tissue in spiral regions.
In both cases the cutting tool is normally a cylinder, whose distal end is perpendicular to the axis of the cylinder. This distal end normally has a cutting edge of serrated construction. In particular, the diameter of the tool is different for each of the two stated solutions.
The object of the present invention is to propose a device and a method which, while avoiding the above-stated disadvantages, make possible in particular the effective removal of bone tissue in the case of spinal endoscopic intervention and allow visual observation of the intervention at any time by the user.